Pole piece for magnetic telegraphones



Nov. 28, 1939. G. E. PERREAULT 2,181,7 7

POLE P IECE FOR MAGNETIC TELEGRAPHONES Filed March 12, 1958 IVSULA 770 /8 x L? T VNSULA T/UN INS UL 4 770A! INS UL 4 7/0 IIVJ (ILA TION INJ' l/Ll TION INVENTOR G. E PERREAULT ATTORNEY Patented Nov. 28, 1939 UNITED STATES PATENT OFFICE POLE PIECE FOR MAGNETIC TELEGRAPHONES This invention netic telegraphones and the tion is t tive life It is,

recording and reproduction should be of very respect disposin of thin magnetic material, the laminations being placed th excess length of sarily very short brings the lateral the tape and the responsive to high so that is supported laterally to provi Great nations if they are stressed ity is gr George E.-

Perreanlt, Bronxville, N. Y.,

assignor to Bell Telephone Laboratories, Incorporated,

New York, N. Y., a corporation of New York Application March 12, 1938, Serial No. 195,429 4 Claims. (01. ire-100.2)

relates to pole pieces 'for magobject of the invenreduce the cost and increase the effecof such pole pieces. I of course, well known that for efficient these pole pieces high permeability and in this very good results have been obtained by g within a non-magnetic shell a plurality laminations of carefully h heat treated the pole piece by non-magnetic material de an enlarged wearing surface.

care must be used in treating the lamiand in assembling them in the shell for appreciably their permeabil eatly reduced and the finished pole piece will be correspondingly less eificient. These pole pieces are therefore quite expensive to manufacture and since the tip portion soon becomes wom with use their useful life is rather short. While it is possible to r'econdition the tips by careful machining this procedure is objectionable from an operating standpoint since change in mechanical adjustments for each par-' tlcular length of pole piece.. Moreover, since the the tip lamination is necesthis method of retipping soon laminations into contact with telegraphone then is no longer frequencies.

According to this invention the pole piece tip which engages the record member comprises a short thin lamination shell by ner and extending back from far enough to the pole held in place within the blocks in the usual manthe pole face only contact the other laminations of When this pole tip becomes worn suitable spacing piece.

the tip lamination and its supporting blocks may be removed and new parts substituted to form a reconditioned pole piece without disturbingthe body portion of the assembly.

As explained in detail in Patent 2,003,968 to Hickman, pole pieces of the laminated type are preferably assembled in pairs and then cut apart to form accurately matched companion pieces.

tips of the two pole pieces may the reconditioning operation pole This accuracy of alignment of the pole be preserved in by removing the worn parts,'mounting the pole pieces in a suitable jig unitary fore.

Accor and reassemblin'g' the pole pieces as a structure which is then cut in two as beding to another feature of the invention,

tapers to a thin tip which it involves 1 a.

the cost of such pole pieces may be further reduced by manufacturing them in the first instance with additional laminations disposed on only one side of the the other side of the magnetic spacer.

In the drawing,

Fig. 1 is a perspective view of a new pole pieces according Fig. 2 shows the pole pieces with their tip portions cut to final shape;

tip lamination and filling shell with a suitable nonpair of I to the invention;

Fig. 3 shows the worn pole pieces assembled in a gig for reconditioning; and

Fig. 4 showsthe reconditioned pole pieces with new tips ready for Fig. 2.

Referring now final shaping as shown in to the drawing, the shell or holder H is preferably of brass formed to a U shape, as shown.

Phenol fibre spacers I2,

and 13 of a thickness equal to one-half the width of the shell are disposed at one side and,

for recording and reproducing pole pieces, the

remaining half of the laminations of some molybdenum permallo to give them a very hi satisfactory method nations is described in man.

The laminations l4 thick tapered at one the fibre blocks l5, l but IE, which is slightly shorter shell is carefully filled with suitable material, such as y, which have been treated gh permeability. One very of preparing such lami- Patent 1,982,810 to Hickmay be about 6 mil-inches end to fit tightly against the short lamination than the block I3, is

preferably much thinner and may be from 0.5 to

2.0 mil-inches thick depending on the frequency response characteristic desired for a given tape speed. Since this lamination must conduct' the entire signal flux to and from the tape, extreme care must be used to avoid bending or otherwise stressing it in placing spacer blocks l3 and This assembly it in position between the 4 I1.

is then given several coats of thin shellac and baked before cutting it along the line l8 to form the companion pole pieces. The

brass housing I l is then cut back a short distance on each pole piece so slightly as shown in of the blocks l3 and that the pole tips protrude Fig. 2. The wearing faces II are then filed off at a slight angle to permit the tip of the lamination It to make good contact with the tape. Since the pole pieces will ordinarily be used on narrow tape, which may be of the order of 50 mil-inches in width, it will also front and back sides so that the completed be necessary to file off the of the protruding pole tip tip has a width slightly less than the width of the tape with which it is to be The tip laminations at this time are firmly held between the spacing blocks and hence this shaping can be accomplished without materially aflecting their permeability.

When it becomes necessary to replace the tips the remaining portions of the old tip lamination and its supporting blocks or spacers are removed, the two housings are clamped in a suitable Jig 20 in accurate axial alignment with the same spacing as in Fig. 2 and a new lamination 26 and supporting and spacing blocks 23 and 21 are inserted. This assembly is then shellacked, baked and cut in two along the line '28 and after shaping the protruding pole tips as before the pole pieces are again ready for use.

This reconditioning technique is, oi course, ap-

plicable also to polarizing pole pieces but for this purpose, due to the higher flux densities used, the laminations are preferably of iron and may be thicker than those used in the translating pole pieces.

What is claimed is:

1. A pole piece for telegraphones having a replaceable tip portion comprising a short thin lamination of magnetic material and lateral supthe material, a short thin holding the material porting members therefor extending into and secured to the body or the pole piece.

'2. A pole piece for telegraphones comprising a body portion of magnetic material, a holder for lamination contacting the material and extending outwardly to form a pole tip} and removable spacers supporting the pole tip in the holder.

3. A pole piece for telegraphones comprising a holder, magnetic material, a spacing member at one side of the holder, and a replaceable tip portion comprising a thin magnetic lamination and lateral supports therefor extending into the holder and securing the lamination in contact with the magnetic material.

4. The method of retipping worn telegraphone pole pieces which comprises removing the worn tip portions, securing two such pole pieces in spaced relation and accurate axial alignment, connecting the pole pieces together with a centrally disposed magnetic lamination and lateral supporting members therefor, and cutting the connecting members to form a new pole face for each pole piece.

v GEORGE E. PERREAULT. 

